Gravel packing process



FIPS-0.1i

Aug. 3, 1954 J. l.. SHEA, JR., ETAL GRAVEL PACKING PROCESS Filed June 30, 195C Patented Aug. 3, 1954 UNITED STATES PATENT OFFICE GRAVEL PACKING PROCESS Application June 30, 1950, Serial No. 171,462

1 Claim.

This invention relates to the gravel packing of wells and more particularly to the placing of a gravel mass behind a perforated casing section and another mass within the perforated casing section and in the annular space between the latter and a well screen.

The gravel packing of open holes, that is, the hole or cavity in a producing formation below the well casing, is a fairly common practice and a method in which the gravel operation is accomplished by reverse circulation is described in the U. S. Letters Patent granted April 23, 1940, to Davis et al., No. 2,198,573. It is, of course, common practice to plug a cased well and then to gun-perforate that portion of the casing within a producing sand so that the oil from the sand formation will pass into the casing through the perforations from which it will flow or be pumped to the surface. A well screen is usually placed within the perforated casing and the upper end of the screen packed off from the casing so that the oil may pass through the casing perforations and then into the screen through its perforations or slits. In this manner most of the sand which would otherwise be produced with the oil is screened oli and only the oil passes to the surface. The problem of successfully gravel packing a well of this type is more diflicult than the packing of an open hole and it is to achieve this result that the method to be described has been provided.

In accordance with the invention the gravel packing is done in two different stages. Briefly, in the rst stage thereof, gravel in a carrier fluid such as oil, or drilling mud, or a combination of drilling mud and oil or water is placed in the casing at the perforated section by pumping the mixture down through a string of tubing which extends approximately to the top of the perforated section. The tubing string is reciprocated up and down after the gravel has settled within the casing and pressure may be simultaneously exerted within the closed casing. The gravel particles are thereby caused to pass through the casing perforations into the space or cavity surrounding the perforated section. The gravel is usually placed in a number of batches of a few cubic feet at a time and the pressure within the casing is noted during each batch operation. The pressure will gradually increase as more of the gravel passes into the cavity and eventually the pressure will reach a predetermined high rvalue indicating that the cavity has been substantially lled with the gravel. The gravel remaining within the casing is then cleaned out 2 by reverse circulation and the tubing string is removed.

In the secondstage of the operation a well screen is lowered on a tubing string and string of wash pipe into position opposite the perforated casing section, the screen being attached at its bottom to the string of wash pipe which projects downwardly through the tubing string which itself is connected to the top of the screen member; After any gravel or debris is washed out of the well through an open valve in the set shoe or bull plug at the bottom of the screen, the val-ve is closed as by pulling the wash pipe slightly upwardly. A mixture of gravel and a carrier uid such as oil is then pumped downwardly through the annular space between the casing and the tubing string and the gravel is deposited between the screen and the perforated casing section while the carrier fluid enters the screen and passes upwardly to the surface through the wash pipe and tubing string. This operation is continued until a sufficient amount of gravel has been placed after which the packer is set at the upper end of the screen and the tubing string and wash pipe removed. Any desired production equipment is then inserted and the well is ready to be produced.

For a better understanding of the invention reference may be had to the accompanying drawing in which Figure 1 is a vertical sectional elevation through a portion of a well showing the rst stage of the graveling operation, and

Figure 2 is a view similar to Figure 1 illustrating the second operation.

With reference to the drawing, a bore hole I0 is shown as provided with a casing I2 usually surrounded with a layer of cement I4. The bore hole I0 and the casing I2 are shown as traversing a producing formation or sand I5. A plug I6 is shown as placed in the casing at or directly below the lower boundary of the producing sand I2 and that portion or section of the casing and cement within the producing sand has been perforated as indicated at I8. Passing downwardly through the casing head or blowout preventer 20 is a string of tubing 22 extending almost to the plug I5 and connected at its upper end as by means of a exible tube 24 to a gravel or squeeze manifold 26. The manifold is connected by means of pipe 28 to the interior of the casing I0 and also by pipe 30 to a pump 32. Connected to the pump line 30 is a gravel hopper 34 having a valve 36 between it and the pipe 30. The manifold 26 is provided with valves 38, 40,

3 42 and 44, the operation of which will be eX- plained hereinafter.

The producing sand I5 is shown as containing a cavity 46 or space from which the sand has been removed as by having flown with the oil into the casing through the perforations I8. If desired, this cavity may be enlarged in a suitable manner as by forcing jets of water or oil outwardly against the sand through the perforations I8. Although a rather large cavity 46 is shown in the drawing, it is to be understood that a cavity is not always necessary for a successful completion of the first stage of the graveling operation. In fact, it has been found that gravel has been successfully placed through casing perforations in new wells where apparently no cavity should exist. Again, it is to be understood that the mere placing of a large volume of gravel behind a perforated casing section does not necessarily mean that a successful graveling operation has been performed. The success of the operation depends rather on thoroughly packing the gravel by completely filling whatever void space there may be behind the casing, regardless of whether it is a large or a small volume.

With the parts as shown in Figure 1, any sand or debris within the casing is washed out as by pumping wash fluid downwardly through the annular space between the casing and the tubing 22, the sand owing upwardly through the tubing. For this operation the valves 36, 40 and 44 will be closed and the valves 42 and 68, open. After the well has been cleaned, a batch of gravel of a suitable size such as from 0.06 to 0.09 inch gauge is introduced into the tubing 22 by pumping it with a carrier fluid through the flexible tube 24 into the tubing. Although a specific size of gravel has been mentioned, it is to be understood that the gravel to be used in each job will be selected according to the grain size of the sand formation and the gravel may vary from approximately 0.05 to 0.25inch in gauge. For this operation the valves 36, 40 and 44 will be open and the valves 38 and 42 will be closed. The circulation of the gravel mixture is continued through the tubing 22 until the gravel arrives at the bottom of the tubing string.

When sufficient time has elapsed for the gravel to be pumped to the bottom of the tubing string, circulation of the carrier fluid is stopped and the gravel is allowed to settle to the bottom of the well. The blowout preventers and valves 36 and 44 are then closed and pressure is applied to the casing by opening valve 42 and pumping in iluid by means of the pumps 32 and the tubing string is reciprocated to agitate the gravel. The gravel particles are thereby squeezed and worked out through the perforations I8 and collected, as is indicated in 48, within the cavity 46. Experience has proved that reciprocation of the tubing string is very important since pressure alone will not force the maximum amount of gravel through the perforations in the casing. The reciprocation of the tubing serves two purposes: (1) it acts as a ram that applies a sudden force or jar to the gravel and causes it to pass through the perforations and (2) this force plus the contact of the pipe with the gravel prevents bridging of the gravel in the perforations. The reciprocation of the tubing string is particularly important when it is necessary to use mud to gravel pack a well. In such cases it is not desirable to squeeze mud into the producing zone as this may prove harmful. Therefore, in performing a job of this type with mud, it is necessary to depend almost entirely on the sudden force or jar caused by reciprocating the tubing string to make the gravel pass outwardly through the perforations in the casing. Only a small amount of pressure such as from 200 to 300 pounds per square inch is applied at the surface in order that force can be transmitted to the gravel. This pressure is not suflicient to pump any appreciable amount of the mud into the formation and consequently is not an important factor in gravel packing under these conditions.

The operation of placing the gravel in about three cubic foot batches is continued until each batch has been squeezed into the cavity 46. The pressure gradually increases with each succeeding batch of gravel and the operation is continued as long as gravel can be forced through the perforations. This operation continues until no more gravel can be placed behind the casing by squeezing and reciprocating the tubing. As an example, in one well which was packed in this manner, the first batch of gravel required 550 pounds per square inch for the gravel to be forced into the cavity. After 27 cubic feet of gravel had been squeezed into the cavity, the pressure was 900 pounds, with 51 cubic feet it was 1,500 pounds, and when 63 cubic feet had been placed, the pressure arose abruptly to 2,200 pounds per square inch and it was known that al1 the gravel possible had been placed in the cavity and the iirst stage of the operation was concluded. Any excess gravel within the casing is then washed out by reverse circulation and the tubing string 22 is removed preparatory to starting the second stage.

As stated above, a large cavity or unconsolidated stratum is not always present behind the perforated casing section, particularly in new wells. Where there is a large cavity, it is not always necessary to reciprocate the tubing string. In such cases the bottom of the tubing is positioned at the top of the perforated zone and the pressure within the casing is raised to squeeze the gravel through the perforations without reciprocating the tubing. The formation will take the gravel at fairly low pressure under such conditions and it is not unusual to be squeezing one batch of gravel through the perforations while another batch is being pumped down through the tubing. However, as has been stated, this procedure is only possible where a large cavity of very loose, unconsolidated sand is present. This procedure is mentioned since it deviates somewhat from the more usual method of squeezing the carrier fluid and reciprocating the tubing string, which is necessary on most jobs.

The second stage operation is illustrated in Figure 2. A liner 52 containing a main slotted portion 54, a circulating slotted section 56 and an upper tell-tale slotted section 58 is inserted in the casing. At the bottom of the liner is a set shoe 66 containing a conventional bottom valve, not shown, and a string of tubing 62 is connected to the top of the liner by means of a stuffing box 64. A string of wash pipe 66 extends down through the tubing and the liner and is connected by means of any suitable connection, threaded or otherwise, to the set shoe 60 in any well known manner in which, when the wash pipe is connected to the set shoe, the aforementioned valve may be held open, while when the wash pipe is disconnected from the set shoe the valve may be closed. A set shoe valve which may be opened or closed from the surface is disclosed in the U. S. Letters Patent No. 2,167,190 granted 5 July 25, 1939, to W. V. Vietti. Any type of letting-in tool may be used on the bottom of the wash pipe for connecting to the set shoe 60 so that the liner can be run into the casing suspended on the wash pipe. The liner is lowered to the bottom with the valve in the set shoe 66 in open position and reverse circulation of washing liquid through the pipe 28 and downwardly between the casing and the tubing string and liner then causes all debris in the casing to be washed through the set shoe 66 and up to the surface through the wash pipe 66. (It should be pointed out that in running a screen or liner to the bottom, it is sometimes necessary to pump fluid downwardly through the tubing and out of the set shoe to wash out any gravel or debris that may be encountered which would otherwise prevent lowering the screen to the bottom.) The wash pipe is then turned in a direction to release it from the set shoe 69 thereby permitting the valve to close, and the wash pipe is pulled slightly upwardly. The calculated volume of gravel required to lill the annulus between the plug I6 and the tell-tale openings 58 is introduced into the casing by pumping the gravel in a carrier fluid inwardly through the pipe 28. The gravel is released from the hopper at a fairly slow rate of about 1/2 cubic foot per minute and pumping is continued until it is certain that all the gravel has fallen to the bottom. In some instances the gravel may be pumped down in batches of a few cubic feet at a time, each batch being pumped to the bottom before another batch is added. Meanwhile the circulating pressure is closely observed at the meter 50 and a gradual increase in pressure is noted as the gravel pack 67 is built up around the main slotted portion 54 of the liner. When sufficient gravel has been deposited to reach the tell-tale slotted portion 58 a sudden pressure increase will be noted indicating that these slots have been covered and that the gravel packing has been completed.

The final operation consists in pulling the wash pipe 66 upwardly until a suitable collapsing tool as shown by the dotted lines 68 engages a conventioned setting device in the packer 1i). The packer is then expanded or set in the conventional manner to seal off the annular space between the liner 52 and the casing. The tubing 62 and the stuinng box 64 is then released from the upper end of the liner, as is described for instance in the aforementioned Davis et al. patent, and the tubing string and wash pipe are removed. Any desired production equipment can n then be inserted and the well will be ready to be produced.

The graveling operation which has been described is done preferably although not necessarily after a well has produced sand. For instance, even though sand troubles are expected when a new completion is made, the well may not be gravel packed until sand has been produced, leaving a cavity around the perforated casing section. In using the method which has been described as much as 270 cubic feet of gravel has been packed around a perforated casing section in some wells. As is well known, a gravel pack offers little restriction to the flow of the fluid into the well bore and by properly graveling substantially all of the sand is maintained in the formation and prevented from flowing upwardly with the oil.

ITO

Although a specific method of well completion has been described, it is to be understood that there are other methods of completion which might be used as the second stage operation after the rst stage has been completed. The more important feature of the invention is the placing of the gravel in the space behind the perforated casing section by squeezing and reciprocating the tubing string, while there is no creen or liner in the hole. This operation is to be followed by the placement of the vscreen within the hole opposite the producing formation and the placing of a mass of gravel in the annular space between the screen and the perforated casing section.

While certain parts of the equipment are illustrated somewhat diagrammatically it is to be understood that these parts do not of themselves form a part of the invention and that any suitable equipment may be used.

Obviously, many other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claim.

We claim:

The method of gravel packing a well having a perforated casing section surrounded by a cavity which comprises plugging the well below said perforated section, circulating wash fluid downwardly between the casing and a string of tubing to wash sand and silt upwardly to the surface through said tubing string, closing the well at the surface, forcing a mixture of approximately 3 cubic feet of gravel and a carrier fluid downwardly through said string of tubing to said perforated casing section, reciprocating said tubing string to agitate the gravel within said casing section while exerting pressure on said mixture to force said gravel through said casing perforations into said cavity, rntthe increase in pressure withinmthwe casing,'repea ing said gravel cirlating and agt'ating operations until the pressure in the casing reaches a.predetermined valjremoving said tubing string, lowering a well screen suspended on a second string of tubing into the casing to a position opposite said perforated casing section, again circulating wash fluid downwardly between the casing and tubing string to wash debris into the lower end of said screen and upwardly through said second tubing string, circulating additional gravel downwardly between said tubing string and said casing, the last-mentioned gravel being deposited in the space between said screen and the perforated casing section, sealing the annular space between the upper end of said screen and said casing and then removing said second tubing string.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,167,190 Vietti July 25, 1939 2,310,397 Coberly Feb. 9, 1943 2,356,769 Layne Aug. 29, 1944 OTHER REFERENCES The Petroleum Engineer for April 1939, pages 

